The present invention relates to blind fastener structures, a system and a method in which a common pin can be used interchangeably with a flush head sleeve and with a low profile protruding or brazier head sleeve and particularly for fasteners which are manufactured of an exotic material such as titanium
The present invention is directed to blind fasteners, namely blind rivets and blind bolts, comprising a pin and a tubular sleeve with the sleeve having a shank and an enlarged head at one end adapted to engage the accessible side of workpieces and with the pin having an enlarged head adapted to engage the opposite end of the shank; a blind head is formed on the inaccessible side of the workpieces in response to a relative axial force applied between the pin and the sleeve. Conventionally the pins are provided with a breakneck groove adapted to fracture at a preselected magnitude of the relative axial force after the blind head has been formed. It is desirable that the fracture occur proximate the outer surface of the sleeve head; to this end the pin and sleeve are provided with stop shoulders adapted to engage and to stop the relative motion between pin and sleeve and, at the same time, to locate the breakneck groove at the sleeve head outer surface. The pin is provided with a lock groove and the sleeve with a lock bore portion in its enlarged head which, when the two are in proper alignment, define a lock pocket adapted to receive a lock collar. In some constructions, the above installation can be performed by a single action tool, see the U.S. Pat. No. 4,432,679 issued Feb. 21, 1984 to Angelosanto et al for "Lock Spindle Blind Fastener for Single Action Application".
In the case of prior blind fastener constructions, whether blind rivets or blind bolts, for a given diameter fastener, the blind side protrusion or clearance of the different sleeves was the same for protruding and flush head fasteners of particular grips when used to join workpieces of a preselected nominal thickness for a given length fastener. In this regard it should be noted that while a particular fastener will be designed to secure a preselected total thickness of workpieces, it will be capable of securing workpieces having a range (grip range) of total thicknesses from a known thickness less (minimum grip) than the nominal thickness (grip) to a known thickness greater (maximum grip) than the nominal thickness. For a given diameter fastener, the nominal grip (designated by numbers 1, 2 . . . ) will vary in uniform steps from one grip to the next; thus for one diameter, the fastener length or usable grip is conventionally varied in 1/16" (0.062") increments, i.e. grips 1 to 4 would be 0.062", 0.125", 0.187" and 0.250", respectively; however, the minimum and maximum grip for that fastener will be on opposite sides of the nominal grip. Thus for example a 1/4" diameter fastener could be manufactured in grip lengths 3 (3/16"), 4 (4/16"), etc. The minimum grip for the 3 grip (3/16" or 0.187") fastener will be 0.156" while the maximum grip will be 0.218". Likewise a 4 grip (1/4" or 0.250") length fastener will have a minimum grip of 0.218" and maximum grip of 0.281". Thus a different length fastener, and hence a different length pin (and sleeve), will be used for each nominal grip (1, 2 . . . ) but will be operative in a range between each grip.
As noted, the present invention applies to both the blind bolt and blind rivet type fastener. Examples of these can generally be seen from U.S. Pat. No. 3,253,495 issued to J. F. Orloff, May 31, 1966, U.S. Pat. No. 4,127,345 issued to Angelosanto et al, Nov. 28, 1978, U.S. Pat. No. 4,230,017 issued to Angelosanto et al, Oct. 28, 1980, and the prior noted U.S. Patent to Angelosanto (supra); the foregoing patents are incorporated herein by reference. Blind fasteners of these types are commonly provided with two sleeve styles, a flush head sleeve and a protruding head sleeve.
With blind rivets the protruding head version was provided to have a desired low profile, brazier type head (see FIG. 6, Angelosanto et al, '017 patent supra). Conventionally pins of different configurations were used for blind rivet flush head and protruding head sleeves.
Thus with such blind rivets, there was no commonality between pins operative for flush head sleeves and pins operative for protruding head sleeves of the same diameter regardless of grip and thus such prior constructions required the use of different pins to accommodate the sleeves with the different head styles. One factor contributing to the use of different pins was that the blind side clearance or protrusion was maintained the same for a given diameter fastener of the flush and protruding head type for a particular grip. However, the fact that different pins were used required the separate manufacture of each such pin including a separate set up time which can be costly especially on short run items. In addition separate tooling configurations are required for the different pin shapes even if the shapes are only slightly different. While this has been a problem with pins of conventional metals, the problem has been compounded with pins of exotic metals such as titanium. Titanium pins usually require more forming and machining operations than pins of other materials.
With blind bolts, however, a common pin structure has been used for two related sleeves of the flush and protruding head type. Thus it has been known to use a common pin for a flush head and protruding head type sleeve for a blind bolt, and, again, as with the blind rivet noted, the blind side protrusion or clearance was maintained constant between the related blind bolt fasteners. However, in order to properly locate the breakneck groove and the lock pocket, this structure required that a non-uniform and at times excessively enlarged sleeve head be utilized in the protruding head design; this resulted in added material and weight. Further, if the sleeve is also to be manufactured of an exotic material such as titanium the extra material required could result in a significant increase in cost, offsetting any manufacturing gains.
In addition the non-uniform sleeve head was difficult to form and more costly to manufacture because of set up and other factors. Also the sleeve head when enlarged, protruded excessively from the outer workpiece surface with which it was engaged which, in aerospace applications, resulted in an aerodynamically undesirable head thickness or height.
In the present invention, a common pin can be used for sleeves with both head styles with the blind side protrusion varying in order to provide the desired location of the breakneck groove at the outer sleeve head surface and the desired orientation for the lock pocket. The protruding head form, however, is of a desired low profile or brazier type with a significantly reduced protrusion from its engaged workpiece surface. The result is a design permitting economy in manufacture (including set up) and a desired low profile, protruding sleeve head style. Thus the present invention facilitates the use of a common pin for flush and protruding heads for blind rivets while permitting the continued use of the desired streamlined protruding head design and for blind bolts while permitting the adoption of the desired streamlined protruding head design.
With prior blind fasteners, it has been common to locate the sleeve stop shoulder near the blind end of the sleeve shank such that in a minimum grip condition the stop shoulder would be located within the confines of the workpieces but near the rear or blind side sheet line. In this case the wall thickness of the sleeve shank within the workpiece openings was dictated by the extra thickness needed to provide a radial step to define the stop shoulder. In the present invention, the sleeve stop shoulder is located near the enlarged sleeve head. This permits a significant reduction in sleeve thickness generally throughout the length of the sleeve shank. In this latter case, the diameter of the pin shank is increased to accommodate the increase in the sleeve shank diameter resulting from the thickness reduction. Since the pin is constructed of a material having a higher shear strength than that of the sleeve, the resultant fastener will have a higher overall shear strength than the fastener of the prior construction in which the sleeve stop shoulder is located near the blind sleeve shank end.
Also with prior constructions, the bulbing of the sleeve to form the blind head was facilitated by using a work hardened or thermally hardened sleeve with bulbing induced to occur at the rear or blind sheet line over a desirable grip range by annealing the shank end of the sleeve to provide a gradient by hardness. Such a construction and procedure is shown in the U.S. Patent to John Orloff, supra. Thus with such constructions annealing was performed at the same fixed location from the sleeve stop shoulder for both of the related flush and protruding head sleeves having the same diameter. In the present invention, the location of the annealed portion will be different for the related flush and protruding head sleeves relative to the stop shoulders, i.e. using a common pin, and that location is not keyed to the sleeve stop shoulder. Now the annealed portion is located at the rear sheet line position on the sleeve shank for the minimum grip condition. The result of the above is a blind fastener system utilizing a uniform or common pin but with a difference in blind side clearance between the related sleeves of flush and protruding head type.
In the past for high strength, lightweight applications it has not been economically desirable to manufacture sleeves of titanium since the sleeves were made by costly machining operations in which a significant amount of the titanium stock material was lost. With the use of certain forms of titanium, sleeves can be more economically made from titanium by cold forming and the gradient of hardness provided by annealing the work hardened shank in a manner similar to that employed for sleeves of ferrous materials. However, by use of the present invention, an all titanium blind fastener can be manufactured with a substantial savings in manufacturing costs for the pin; in addition the manufacture of sleeves, with uniform head shapes, from titanium lends itself to further economies in manufacturing via cold forming, set up and in material cost via reduced head size.
Thus it is an object of the present invention to provide a blind fastener construction, system and method of the above described type in which a common pin can be utilized for related sleeves with flush and protruding heads resulting in economy of manufacture.
It is another object of the present invention to provide a blind fastener construction, system and method of the above described type in which the blind side protrusion of the fastener will be varied for the same diameter fasteners with sleeves of the different head styles utilizing a common pin construction for each.
It is another object to provide a blind fastener construction in which the sleeve stop shoulder of increased wall thickness is located proximate the sleeve head whereby the remainder of the sleeve shank is of a reduced wall thickness resulting in the pin and sleeve combination of the fastener to have a higher overall shear strength.
It is an object of the present invention to provide a blind fastener in which a hardened sleeve is used and is annealed at the rear sheet line minimum grip position to facilitate bulbing over a desired grip range.
It is another object of the present invention to provide a blind fastener system, method and construction in which a common pin can be used for related protruding and flush head sleeves of the same diameter with the protruding head being uniform for different length sleeves of the same diameter and with the protruding head having a desired low profile configuration.
It is still another object to provide a blind fastener in which a titanium sleeve is manufactured by cold forming with a gradient of hardness provided at the desired shank location by annealing at the rear sheet line minimum grip position to facilitate bulbing over a desired grip range.
It is another object to provide a blind fastener system, method and construction of a substantially all titanium (or other exotic material) construction in which a common pin can be used for related protruding and flush head sleeves of the same diameter and in which the protruding head is of a uniform shape for different length sleeves of the same diameter and with the sleeve being cold formed with the protruding head having a desired low profile configuration.
It is a general object of the present invention to provide a novel blind fastener construction, system and method.
Other objects, features, and advantages of the present invention will become apparent from the subsequent description and the appended claims, taken in conjunction with the accompanying drawings.